Redundancy is a technique that is currently employed in digital computer systems to achieve fault tolerance. Redundant components, such as logic arrays, memory circuits and processors, have been used which are driven by a master clock for the system. A more effective fault tolerant computer system can be obtained if the redundant components of the computer system are divided into groups of elements, with each group having its own synchronized clock. In such a system, if a clock fails, a standby clock can be switched in to take its place. When redundant clocks are employed, they must remain synchronized within close tolerances. Excessive amounts of time that occur between the logic triggering edges of the two clocks which result in "skew faults" must be detected to insure that the clock system is operating properly. The present invention provides a novel implementation of skew fault detection which is suitable for redundant clock systems and which has self-checking capabilities that monitor the failure of component parts of the skew fault detection system.